Introduction 

In the chronic illness sphere, patient adherence to prescribed medications is a major predictor of successful outcomes. Previous studies have shown that 50-60 percent of patients with chronic illnesses miss doses, take the wrong dosages, or withdraw from treatment in the first year after being diagnosed. Lack of medication adherence is associated with poorer health outcomes, and 125,000 deaths each year in the United States are associated with nonadherence. Estimates show that between $100-$300 billion of avoidable healthcare costs can be attributed to nonadherence in the US annually. To combat patient nonadherence, researchers and policymakers should craft solutions that address the many different factors that affect it, including patient-, prescriber-, and medication-related factors.   

 Measures of Adherence 

Three separate measures of patient adherence have been identified and can be used to predict health outcomes.  

Persistence describes how long patients take a drug before either switching to a new one or ceasing treatment entirely. The CDC defines persistence as the “duration of time a patient takes a medication from initiation to discontinuation of therapy.” This can be measured by quantifying how many patients continue to fill an existing prescription. 

Compliance deals with how closely patients follow prescription plans assigned by their physicians. For instance, a compliant patient is one who fills their prescription dose on a schedule recommended by the product label or provider. This measure deals with the patient’s passive following of providers’ orders on a day-to-day basis.   

Adherence itself is a combination of both compliance and persistence. Adherent patients continue to fill their existing prescriptions on schedules recommended by the approved product label. This also includes following dosing, frequency, specific timing, and conditions such as with or without food that are recommended by their physicians. Most studies consider patients to be adherent if at least 80 percent of their doses are fulfilled according to the recommended schedule.  

Variation in Adherence 

Patient adherence varies greatly across the spectrum of chronic disease categories. Studies show that 37 to 74 percent of patients do not adhere to treatment regimens recommended by product labels and providers.  Contrary to previous studies, newer data shows that as the severity of the condition gets worse, patient adherence rates increase. For example, patients with multiple sclerosis or HIV – two of the most severe chronic conditions – had higher median twelve-month adherence rates than the other chronic diseases examined. This suggests that patients with more serious chronic diseases are more likely to be both persistent and compliant in following treatment protocols.  

Racial and ethnic disparities in medication adherence also exist among chronic disease patients. Minority patients typically have higher prevalence rates of chronic diseases, worse access to medical care, and greater financial constraints in treating their conditions. Even after controlling for socioeconomic characteristics, average adherence rates of Black and Hispanic patients were 4.8-6.5 percentage points lower than White patients with similar chronic conditions. Specifically, Black and Hispanic patients were shown to take medications less consistently than White patients, but they were not shown to be at a higher risk of discontinuing medication entirely. This means that while compliance and adherence rates differ, persistence remains unaltered by racial and ethnic differences. These results also suggest that efforts to reduce adherence disparities should focus on improving day-to-day medication adherence rather than the cessation of therapy altogether.  

Factors Affecting Adherence 

Patient-Related Factors: 

Patient-related factors substantially affect the rates of patient adherence. Objective severity of disease has already been noted as a factor in adherence prediction, but patients’ subjective perceptions and awareness of chronic disease severity is also an important predictor. Nonadherence was found to be more than 1.5 times likely in patients who did not perceive their chronic condition as severe. Patient cost sharing has also been shown to impede adherence. One study found that patient treatment cessation increased four-fold when out-of-pocket cost sharing payments were $500 per treatment vs. $100 or less per treatment. Support systems made up by families and community members also influence whether a patient is adherent. Patients were 69-75 percent more likely to be medically adherent when they perceived themselves as having a strong support system. Providing chronic patients with caregiver support may be one way to build up a support system and encourage adherence. 

Prescriber-Related Factors: 

Adherence can also be affected by the expertise and quality of providers prescribing treatments, which can lead to variations in the percentage of patients adherent by physician. For psoriasis – a chronic autoimmune skin condition – patient adherence varied between less than 20 percent to over 80 percent for different physicians that treated patients. Patient-physician communication is significantly correlated with patient adherence as there is a 19 percent higher risk of nonadherence among patients whose physicians poorly communicate treatment plans. Routinely training physicians in effective patient communication skills may be one solution to increasing adherence as it can improve the transmission and retrieval of important medical information, facilitate patients’ involvement in their own health care, and offer patients support in their treatment regimes. 

Medication-Related Factors:  

Lastly, medication-related factors can have an impact on patient adherence in treatment. Patient adherence is more likely to occur if the route of administration is convenient, such as oral medication. In asthma patients, adherence was higher in patients taking oral medications than patients using a more complex inhaler. Though adherence does not appear to correlate with the number of medications taken, the number of doses per day of all prescribed medications does seem to have an effect. Nonadherence rates increase with an increase in the frequency of doses per day, from 30% for twice daily to 70% for four times daily. Side effects from medication can also threaten patient adherence. Adverse side effects can produce physical discomfort in patients and lead to skepticism in terms of medication efficacy. Through continuous scientific discovery, simplifications in routes of administration, improvements in medication dosing frequency, and reductions in adverse side effects will likely lead to improved adherence in chronic pain patients.  

Conclusion 

Like many other issues in healthcare, patient adherence is a complicated problem and is affected by factors that range from the healthcare system to patients themselves. With this complexity, though, comes the opportunity for significant improvements in health outcomes. Researchers and policymakers should come together to identify policy solutions most likely to address barriers in adherence.